1. Field of the Invention
The invention generally relates to a device for the surgical treatment of spinal fractures or for straightening the spine in the surgical treatment for deviations of the spinal column, especially scoliosis. In particular, the present invention relates to a hook assembly for a Harrington compression rod, or a transverse traction device which are affixed to the spine.
2. Description of the Prior Act
Scoliosis is the lateral deviation of the spinal column. The spinal curvature which results from scoliosis is generally defined on the basis of specific reference points. In particular, the extreme upper and lower vertebrae and the most displaced vertebra are of particular interest. The extreme upper and lower vertebrae are those which are the most inclined relative to the median longitudinal axis of the torso. The two planes within which the extreme upper and lower vertebrae can be found define the scoliotic angle. The most displaced vertebra is defined as the vertebra which is the farthest from the median axis of the torso.
When the scoliotic angle of curvature exceeds a given limit of approximately 35.degree.-50.degree., it becomes necessary to consider surgical treatment of the scoliosis. The surgical treatment is known as arthrodesis and consists of fusing together the vertebrae of the scoliotic curvature, after correcting the scoliotic curvature to the maximum possible extent. Such correction can be accomplished prior to the operation by continuous traction of the spine or by corrective plaster casts.
However, it is during surgery that the correction is completed and finalized. For this purpose, a solid metallic rod with hooks is placed in the concavity of the curvature and a threaded rod with hooks is placed on the convexity of the curvature. These rods straighten the spine and maintain the correction until arthrodesis is attained by means of autogenous bone graft. The implants used most often to correct curvature during surgery are known as the Harrington distraction system and the Harrington compression system, illustrated in FIG. 1.
The distraction system consists of two metallic anchoring devices 116 and 117 of the hook type which are attached to the vertebrae 4 which comprise the spinal column, generally referred to by reference character 1. A notched metal rod 115 serves as a stay and permits the spacing between the hooks 116 and 117. One of the ends 118 of rod 115 is usually notched in such a manner as to permit the distance between anchoring devices 116 and 117 to be adjusted by means of a spreading instrument. Generally, the upper anchoring element 116 is intended for fastening toward the upper end of the spine and is hooked onto a dorsal vertebra 9. Usually, the hook of element 116 is directed upward and shaped in such a manner as to permit its insertion between the articular facets of two adjacent vertebrae. The hook of element 116 penetrates into the interarticular space and is supported on the vertebra.
Similarly, a lower anchoring element 117 is intended to be fastened at the lower end of the spine and is often supported on a lumbar vertebra 10. It is contemplated that the hook associated with element 117 is directed downwardly and supported on the lamina of the lumbar vertebra between the spinous process and the articular facet. In the illustrated example, vertebrae 9 and 10 are considered to be the extreme vertebrae.
The compression system consists of two or more metallic anchoring devices 111 and 112 of the hook type which are attached to selected transverse processes of vertebrae 4 which are situated on the convex side of the scoliotic curvature. Threaded metal rod 113 serves as a stay and permits spacing between the hooks 111 and 112. Hooks 111 and 112 usually face each other and slide freely along threaded rod 113. These hooks are adjusted by means of nuts 114 so as to effect compression of the convexity of the scoliotic curvature. It is understood that more than two hooks and nuts can be used to achieve the desired amount of compression.
Thus, by the application of Harrington distraction and compression systems, the straightening of the scoliotic curvature can be effected and maintained. Vertebral arthrodesis is then achieved by exposing the posterior arches of the vertebrae and attaching autogenous spongy bone with the Harrington devices left in place.
FIG. 2 is an illustration of a patient suffering from scoliosis schematically represented from the rear. The spinal column 1 is visible and indicated schematically by rectangles or trapezoids. The patient illustrated in FIG. 2 exhibits a scoliosis involving a deviation of the vertebrae to the right. The scoliotic curvature can be defined on the basis of the top vertebra 2 and the bottom vertebra 3 of the deviation, and the vertebrae 4 which are located at the peak of the curvature. It is noted that the vertebrae 2 and 3 are those which are most strongly inclined relative to the median longitudinal axis M--M of the body, while vertebrae 4 are those which are farthest from that axis. Angle .alpha. is thus a characteristic of the scoliotic curvature. When the angle .alpha. exceeds a limit of approximately 35.degree.-50.degree., it is often necessary to resort to arthrodesis and to install Harrington distraction and compression rod systems, as illustrated in FIG. 1.
However, the Harrington distraction and compression systems are not totally effective in supporting the peak vertebrae 4 which are further away from the axis M--M than the other vertebrae and cannot fully accomplish straightening of the scoliotic curvature. Accordingly, transverse tensioning devices as illustrated in FIGS. 3 and 4 have been suggested by French Pat. No. 2,244,446. Such a transverse tensioning device makes use of (1) a compression rod 11, similar to the Harrington compression rod, and (2) a tensioning element 12. Obviously, the intent of the Harrington distraction rod 5 is to separate the vertebrae apart from each other. The basis of the transverse tensioning device is a tensioning element 12 which is supported by the compression rod 11 on the side of the vertebrae most displaced by the curvature and connected to the other side of the spine by the Harrington distraction rod 5. Preferably, the tensioning means is adjustable so that the peak of the scoliotic curvature can be pulled toward the distraction rod 5, resulting in a better correction of the curvature and a better preservation of the correction obtained. It is contemplated that a transverse tensioning device results in reduction of the lateral displacement of the most displaced vertebrae, completion of the correction obtained by the longitudinal Harrington distraction rod, and relief of the load on the supporting vertebrae.
Generally, the transverse tensioning devices of the prior art have been comprised of compression rod 11 and tensioning element 12, the first of which is intended to be supported on two vertebrae 4 which are closest to the peak of the scoliotic curvature, and the second of which permits the first to be brought nearer to the metallic distraction rod 5.
Compression rod 11 is generally comprised of a threaded rod 13, at one end of which is permanently fastened a hook 14. This rod 13 passes freely through another hook 15 which is held in place by nuts 16. Hook 15 slides along rod 13 and faces hook 14. Hook 14 has a rounded and beveled end 17 which allows it to be supported, from top to bottom, by the transverse processes of the upper vertebra 4 of the peak, after cutting of the costotransverse ligament. Hook 15 passes from the bottom to top beneath the transverse process of the lower vertebra 4 of the peak. Nut and locking nut 16 permit hooks 14 and 15 to be brought closer to each other and to be tightened in such a way as to effect a firm transverse grip. Hook 15 is finally locked into position by means of a set screw S which jams the threads of rod 11. Hooks 14 and 15 are attached to the transverse processes of vertebra 4 which are situated on the convex side of the scoliotic curvature.
Tensioning element 12 comprises a threaded rod having one end which is permanently fastened to hook 18. The rod passes freely through another hook 19 which is held in place on the rod by nuts 21. Hook 19 is able to slide along the rod and faces hook 18. Hook 18 engages rod 13 and hook 19 engages Harrington rod 5. By screwing nut and locking nut 20 along the rod hooks 18 and 19 approach each other and the peak vertebrae 4 are made to approach median axis M--M. This allows better correction of the scoliotic curvature. Hook 19 is finally locked into position by means of a set screws which jam the threads of element 12. It is noted that elements 11 and 12 are located at the posterior side of the spine, element 12 being in contact with the spongy graft 21 necessary for this arthrodesis so as to reinforce the solidity of the arthrodesis.
The surgical techniques used in employing the transverse traction device illustrated in FIGS. 3 and 4 are outlined in more detail by Dr. Cotrel in his article entitled "New Techniques for the Treatment of Idiopathic Scoliosis," International Orthopedics, Spring, 1978, pp. 247-265.
The basic problems with the above described transverse traction system are as follows:
1. It is difficult to apply.
2. It requires the use of additional instruments other than those commonly available to spinal surgeons familiar with the Harrington procedure.
3. It provides for the use of tiny set screws to positively locate hooks 15 and 19 on elements 11 and 12. Such set screws must be cut off flush with the hooks, thereby risking the loss of a portion of a set screw in the human body.
4. Hook 18 of element 12 does not positively locate on element 11 and is subject to slippage.